Lack of adaptive response to low doses of ionizing radiation in human lymphocytes from five different donors

Abstract

Various investigators reported a reduced yield of chromosome and chromatid aberrations in short-term cultures of human lymphocytes if a ‘challenge’ exposure to ionizing radiation was preceded by an ‘adaptive’ exposure. In order to examine the cell cycle dependence of the ‘adaptive response’, chromosome and chromatid aberration yields were estimated after challenge doses in the G 1, S or G 2 phase of lymphocytes which had been adapted in the early G 1 phase. On testing two donors no protective adaptive response was found. Blood samples of four donors were tested for their capability to evoke the adaptive response in a standard experiment with the adaptive dose in the S phase and the challenge dose in the G 2 phase. A synergistic response occurred in one out of two similar experiments performed with the same blood sample. The three other blood samples tested did not respond. Apparently these data indicate a high frequency of human lymphocyte cultures that do not display an adaptive response.